Image guided dental implant planning systems design and make surgical guides, which have drilling holes and will fit onto patients' anatomy so that the implants can be placed at the planned locations and orientations. The basic technology and procedures can be found in publications of Azari, Jabero, Spector, Tardieu, et al.
Many treatment planning users and research groups have noticed that the accuracy can be a great concern for image guided implant dentistry (Oyama, Oguz, Giovanni, et al). In a research of Schneider, et al., an electronic literature search complemented by manual searching was performed to gather data on accuracy and surgical, biological and prosthetic complications in connection with computer-guided implant treatment. From 3120 titles after the literature search, eight articles met the inclusion criteria regarding accuracy and 10 regarding the clinical performance. Meta-regression analysis revealed a mean deviation at the entry point of 1.07 mm (95% CI: 0.76-1.22 mm) and at the apex of 1.63 mm (95% CI: 1.26-2 mm). No significant differences between the studies were found regarding method of template production or template support and stabilization. Early surgical complications occurred in 9.1%, early prosthetic complications in 18.8% and late prosthetic complications in 12% of the cases. Implant survival rates of 91-100% after an observation time of 12-60 months are reported in six clinical studies with 537 implants mainly restored immediately after flapless implantation procedures.
A typical methodology of the accuracy investigation can be found in the paper of Pettersson, et al. Ten maxillae and 7 mandibles, from completely edentulous cadavers, were scanned with CT, and 145 implants (Brånemark RP Groovy) were planned with software and placed with the aid of a CAD/CAM-guided surgical template. The preoperative CT scan was matched with the postoperative CT scan using voxel-based registration. The positions of the virtually planned implants were compared with the actual positions of the implants. The mean measurement differences between the computer-planned implants and implants placed after surgery for all implants placed were 1.25 mm (95% CI: 1.13-1.36) for the apex, 1.06 mm (95% CI: 0.97-1.16) for the hex, 0.28 mm (95% CI: 0.18-0.38) for the depth deviation, 2.64 degrees (95% CI: 2.41-2.87) for the angular deviation, and 0.71 mm (95% CI: 0.61-0.81 mm) for the translation deviation. Interestingly, the results demonstrated a statistically significant difference between mandibles and maxillae for the hex, apex, and depth measurements in the variation between the virtually planned implant positions and the positions of the implants placed after surgery with a CAD/CAM-guided surgical template. Other literatures related to implant accuracy or the fit of surgical guides are found to use the similar approach. While such research does reveal some accuracy issues, the investigation method is problematic. The researchers usually have only one or two systems, they usually don't try to address where the errors are from by looking at the workflow and image processing approaches, and moreover the research procedures like the afterward registration mentioned above can introduce errors as the treatment planning software does.
The errors of surgical guides come from the design and manufacturing process. The prior art to make surgical guides can be found in Pompa U.S. Pat. No. 5,320,529, Gelb U.S. Pat. No. 5,538,424, Swaelens U.S. Pat. No. 5,768,134, and Gao's U.S. patent application Ser. Nos. 12,776,544, 12,795,045. The published software systems, such as SimPlant™, NobelGuide™, EasyGuide™, etc, utilize similar techniques. Swaelens described the commonly used method, which features so called ‘Dual Scan’ and surgical guide made by SLA. The dual scan protocol uses a radiographic guide that has radiographic markers. A patient is CT-scanned wearing a radiographic guide, and then the guide is scanned separately. The two CT scan datasets are loaded and registered together. Implants are simulated with the patient CT scan, and drill holes are made on the digital model of the radiographic guide, which results in a surgical guide. The surgical guide is later on made with SLA or 3D printing technology. Any manufacturing or data processing error in this workflow can lead to the inaccuracy or misfit of the surgical guide.
Some conclusions one can draw from the workflow and the research in the guide accuracy area are: some errors are inherent to the workflows and underlying technologies; depending on patients' oral-dental structures and the restoration techniques, some cases can tolerate bigger inaccuracy, some cannot; even though the errors of 1 mm or more sounds substantial, the implant survival rate is actually good; more work needs to be done to better breakdown the error sources, and tackle the accuracy issues one by one, or to improve the workflows; since errors can not be avoided or hard to control, it can be very beneficial to evaluate a plan against maximum error conditions. This disclosure is relevant to the evaluation of treatment plans as errors are concerned.
The placement of an implant is often evaluated in a few ways. The most common tool is so-called bone quality analysis. The neighborhood bone structure of an implant is displayed with a color scheme so that the CT Hounsfield unit values are mapped into different colors. The users can justify the sufficiency of bone structure by looking at the neighborhood colors. In addition, a safety zone can be defined for an implant, which is typically a 2-3 mm offset of the implant surface. It is mainly used to check the interferences between an implant and adjacent teeth, other implants or nerve channels.
In the published systems, the evaluations of treatment plans do not include “what-if” simulations, or error simulations. The objective of this invention is to introduce a mechanism to simulate various error conditions, and integrate such error simulation into the evaluation process of a treatment plan.